U.S. patent application number 11/157174 was filed with the patent office on 2006-01-05 for light emitting element and method of making same.
This patent application is currently assigned to Toyoda Gosei Co., Ltd.. Invention is credited to Yoshinobu Suehiro, Satoshi Wada.
Application Number | 20060001035 11/157174 |
Document ID | / |
Family ID | 35512964 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060001035 |
Kind Code |
A1 |
Suehiro; Yoshinobu ; et
al. |
January 5, 2006 |
Light emitting element and method of making same
Abstract
A light emitting element has: a semiconductor layer having a
light-emitting layer; a first electrode; a second electrode; an
insulation layer that is formed on a mounting face side of the
semiconductor layer; and a first terminal and a second terminal
that are formed on a surface of the insulation layer corresponding
to the first electrode and the second electrode, respectively. The
first electrode and the second electrode are formed on the mounting
face side of the semiconductor layer. The insulation layer has a
first opening and a second opening, and the first electrode and the
second electrode are electrically connected through the first hole
and the second hole, respectively, to the first terminal and the
second terminal.
Inventors: |
Suehiro; Yoshinobu;
(Aichi-ken, JP) ; Wada; Satoshi; (Aichi-ken,
JP) |
Correspondence
Address: |
MCGINN INTELLECTUAL PROPERTY LAW GROUP, PLLC
8321 OLD COURTHOUSE ROAD
SUITE 200
VIENNA
VA
22182-3817
US
|
Assignee: |
Toyoda Gosei Co., Ltd.
Aichi-ken
JP
|
Family ID: |
35512964 |
Appl. No.: |
11/157174 |
Filed: |
June 21, 2005 |
Current U.S.
Class: |
257/91 ; 257/103;
257/99; 438/22 |
Current CPC
Class: |
H01L 33/20 20130101;
H01L 2924/0002 20130101; H01L 2924/0002 20130101; H01L 2933/0016
20130101; H01L 33/38 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/091 ;
257/103; 257/099; 438/022 |
International
Class: |
H01L 29/205 20060101
H01L029/205; H01L 21/00 20060101 H01L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2004 |
JP |
2004-184028 |
Aug 31, 2004 |
JP |
2004-252499 |
Claims
1. A light emitting element, comprising: a semiconductor layer
comprising a light-emitting layer; a first electrode that is
defined corresponding to the light-emitting layer to supply power
to the light-emitting layer; a second electrode that is defined as
a counter electrode of the first electrode; an insulation layer
that is formed on a mounting face side of the semiconductor layer;
and a first terminal and a second terminal that are formed on a
surface of the insulation layer corresponding to the first
electrode and the second electrode, respectively, wherein the first
electrode and the second electrode are formed on the mounting face
side of the semiconductor layer, the insulation layer comprises a
first opening and a second opening that are formed corresponding to
the first electrode and the second electrode, respectively, and the
first electrode and the second electrode are electrically connected
through the first hole and the second hole, respectively, to the
first terminal and the second terminal.
2. The light emitting element according to claim 1, wherein: the
second electrode comprises a narrow line, and the narrow line has a
width of 50 .mu.m or less.
3. The light emitting element according to claim 1, wherein: the
first terminal and the second terminal have a width of 100 .mu.m or
more.
4. The light emitting element according to claim 1, wherein: the
second terminal has an area greater than the second electrode.
5. A light emitting element, comprising: a semiconductor layer
comprising a light-emitting layer; a first electrode that is
defined corresponding to the light-emitting layer to supply power
to the light-emitting layer; a second electrode that is defined as
a counter electrode of the first electrode; wherein the first
electrode and the second electrode are formed on the mounting face
side of the semiconductor layer, and the light-emitting layer and
the first electrode are surrounded by the second electrode.
6. The light emitting element according to claim 5, wherein: the
light-emitting layer surrounded by the second electrode comprises
an uneven end face.
7. The light emitting element according to claim 5, wherein: a
plurality of the light-emitting layers and a plurality of the first
electrodes corresponding the plurality of the light-emitting layers
are surrounded by the second electrode.
8. The light emitting element according to claim 1, wherein: the
first electrode has a surface area ratio of 60% or more relative to
the light emitting element.
9. The light emitting element according to claim 5, wherein: the
first electrode has a surface area ratio of 60% or more relative to
the light emitting element.
10. The light emitting element according to claim 1, wherein: the
light-emitting layer is formed symmetrical with respect to axes
that are orthogonal to each other with respect to a center axis of
the light emitting element.
11. The light emitting element according to claim 5, wherein: the
light-emitting layer is formed symmetrical with respect to axes
that are orthogonal to each other with respect to a center axis of
the light emitting element.
12. The light emitting element according to claim 1, wherein: the
second electrode comprises a part formed in a region of the first
electrode.
13. The light emitting element according to claim 5, wherein: the
second electrode comprises a part formed in a region of the first
electrode.
14. The light emitting element according to claim 1, wherein: the
semiconductor layer comprises a GaN-based semiconductor, the first
electrode is a p-type electrode, and the second electrode is an
n-type electrode.
15. The light emitting element according to claim 5, wherein; the
semiconductor layer comprises a GaN-based semiconductor, the first
electrode is a p-type electrode, and the second electrode is an
n-type electrode.
16. A light emitting element, comprising: a semiconductor layer
comprising a light-emitting layer; and an n-type electrode and a
p-type electrode to supply power to the light-emitting layer,
wherein the n-type electrode and the p-type electrode are provided
at a periphery of the semiconductor layer that has a width smaller
than an entire width of the light emitting element.
17. The light emitting element according to claim 16, wherein: the
periphery is formed by partially removing the semiconductor layer
in a same direction as a stack direction of the semiconductor
layer.
18. The light emitting element according to claim 16, wherein: the
n-type electrode and the p-type electrode are provided at the
periphery of the semiconductor layer through an insulation layer
comprising a transparent material with a refractive index different
from the semiconductor layer, and the n-type electrode and the
p-type electrode are electrically connected to an n-type layer and
a p-type layer, respectively.
19. The light emitting element according to claim 16, wherein: the
n-type electrode and the p-type electrode are, in mounting the
light emitting element, electrically connected at a part exposed to
the periphery of the semiconductor layer while allowing a sapphire
substrate as an underlying substrate of the semiconductor layer to
be in close contact with a mounting face.
20. The light emitting element according to claim 16, wherein: the
n-type electrode and the p-type electrode are electrically
connected to an external circuit at a part exposed to the periphery
of the semiconductor layer while allowing the semiconductor layer
to be in close contact with a mounting face.
21. The light emitting element according to claim 16, wherein: the
n-type electrode and the p-type electrode comprise an n-type
electrode provided inside of a hole formed in the semiconductor
layer, and a p-type electrode provided outside of the semiconductor
layer.
22. The light emitting element according to claim 16, wherein: the
semiconductor layer comprises a group III nitride-based compound
semiconductor.
23. A method of making a light emitting element, comprising: a
semiconductor layer formation step of forming a semiconductor layer
comprising a light-emitting layer by stacking a semiconductor
material on a wafer underlying substrate; a semiconductor layer
removal step of partially removing the semiconductor layer in a
predetermined width and a predetermined depth from a surface of the
semiconductor layer to formed an exposed portion; an electrode
formation step of forming electrodes to supply power to an n-type
layer and a p-type layer of the semiconductor layer at the exposed
portion; and an element formation step of cutting the underlying
substrate with the semiconductor layer into a light emitting
element to allow the electrodes to be exposed to a periphery of the
light emitting element.
24. The method according to claim 23, wherein: the electrode
formation step comprises: an insulation layer formation step of
forming an insulation layer to cover a surface of the semiconductor
layer and the exposed portion; an insulation layer removal step of
removing the insulation layer while securing an insulation between
the n-type layer and the p-type layer to form electrode formation
regions corresponding to the n-type layer and the p-type layer; and
an-external electrode formation step of forming external electrodes
to be connected to the n-type layer and the p-type layer in the
corresponding electrode formation regions.
25. The method according to claim 24 wherein: the external
electrode formation step comprises: a first external electrode
formation step of forming a first external electrode to be
connected to the n-type layer; and a second external electrode
formation step of forming a second external electrode to be
connected to the p-type layer.
26. The method according to claim 24 wherein: the external
electrode formation step comprises: a first external electrode
formation step of forming a first external electrode to be
connected to the n-type layer; and a second external electrode
formation step of forming a second external electrode to be
connected to the p-type layer, wherein the first external electrode
formation step and the second external electrode formation step are
conducted simultaneously.
27. The method according to claim 23 wherein: the semiconductor
layer formation step comprising a step of forming a contact
electrode made of a light reflecting material on the p-type
layer.
28. The method according to claim 23 wherein: the semiconductor
layer formation step comprising a step of forming a contact
electrode made of a light transmitting material on the p-type
layer.
Description
[0001] The present application is based on Japanese patent
application Nos. 2004-184028 and 2004-252499, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a light emitting element and,
particularly, to a light emitting element that has an increased
emission area relative to the element's surface area and prevents
unevenness in light distribution so as to increase brightness
thereof. Also, this invention relates to a light emitting element
that has an excellent mounting performance, a high reliability in
electrical connection, and a heat radiation performance as well as
having an increased emission area relative to the element's surface
area. Further, this invention relates to a method of making the
light emitting element thus featured while using the conventional
apparatus without requiring any advance technique.
[0004] Herein, a light emitting element includes a light emitting
device, a light emitting diode (LED) and an LED element.
[0005] 2. Description of the Related Art
[0006] A light emitting element (herein also referred to as LED
element) is known in which a group III nitride-based compound
semiconductor is grown on a transparent underlying substrate such
as sapphire. Also, it is known that the LED element is flip-chip
mounted on a mounting board to extract light from the underlying
substrate side since the underlying substrate is transparent (for
example, see JP-A-2002-232016, paragraph 0005).
[0007] JP-A-2002-233016 discloses a flip-chip mounting method that
an LED element is carried onto a submount board with bumps attached
corresponding to a p-electrode and an n-electrode of the LED
element while being in vacuum contact with a vacuum head. In
process of the method, the posture of the LED element is controlled
such that the n-electrode of the LED element is mounted on the
p-electrode bump of the submount board and p-electrode of the LED
element is mounted on the n-electrode bump of the submount board.
Then, by applying ultrasonic vibration to the LED element, the LED
element is pressure-bonded to the submount board while allowing the
bumps to be pushed down.
[0008] FIG. 12 is a perspective view showing an electrode forming
surface of the LED element. The LED element 30 comprises: a
transparent sapphire substrate 31; a buffer layer 32 formed on the
sapphire substrate 31; an n-type semiconductor layer 33 formed on
the buffer layer 32; a light-emitting layer 34 formed on the n-type
semiconductor layer 33 to emit light based on the radiative
recombination of hole and electron; a p-type semiconductor layer 35
formed on the light-emitting layer 34; the n-electrode 36 which is
formed on part of the n-type semiconductor layer 33 exposed by
partially etching the p-type semiconductor layer 35 to the n-type
semiconductor layer 33; and the p-electrode 36 which is formed on
the p-type semiconductor layer 35 and whose surface area is defined
except the exposed part of the n-type semiconductor layer 33.
[0009] However, in the above LED element, the p-electrode and the
n-electrode each needs to have a certain electrode area to
facilitate the wire bonding in the flip-chip mounting. Especially,
since the p-electrode area corresponding to the emission area is
reduced due to the n-electrode area, the rate of the emission area
relative to the element's surface area must be reduced. Therefore,
a large current cannot be applied thereto since the current density
of the light-emitting layer becomes too high.
[0010] Further, since about 1/4 of the element's surface area
becomes nonradiative portion due to the n-electrode area, a
non-uniform light pattern is generated. When the LED element is
used in combination with a convergence optical system, the
non-uniform light pattern is radiated and focused. Therefore, it is
difficult to enhance the brightness or to improve the light
distribution.
[0011] To solve the above problems, an LED element is suggested in
which electrodes for applying a voltage to an n-type semiconductor
layer and a p-type semiconductor layer of the LED element are
provided on the side face of the LED element (for example, see
JP-A-B-102552, paragraphs 0024 to 0032 and FIG. 1 thereof).
[0012] JP-A-8-102552 (FIG. 1) discloses the LED element that
insulation layers of SiO.sub.2 are formed on the side faces of a
semiconductor layer and a sapphire substrate. One of the insulation
layers is etched at part corresponding to an end face of a p-type
GaN layer at the top of semiconductor layers of the LED element,
and the other of the insulation layers is etched at part
corresponding to an end face of an n-type GaN layer. A p-electrode
and an n-electrode each are formed on the insulation layer as a
conductive film electrically connected to the p-type GaN layer and
the n-type GaN layer through the etched part.
[0013] In the above LED element, since no electrode is formed on
the surface (light extraction surface) of the semiconductor layer,
light emitted from the light-emitting layer can be efficiently
radiated upward without being blocked by any electrode. Further,
since the area of the light-emitting layer is not reduced by
etching, the light-emitting layer can have the same area as the
sapphire substrate. Therefore, the mount of light radiated from the
top face of the semiconductor layer increases and thereby the
emission intensity can be enhanced.
[0014] However, the LED element of JP-A-8-103055 needs a process
that, after a wafer is fabricated by forming the semiconductor
layers on the sapphire substrate and then the wafer is diced into
chips, the insulation layer is partially etched and the p- and
n-electrodes are formed at the etched part through which they are
electrically connected to the p-type GaN layer and the n-type GaN
layer. Thus, since each chip needs to be processed by using a
microscopic and advanced technique, it is difficult to produce the
LED element in mass production. Further, in the LED element,
although the electrical connection performance is enhanced, the
heat radiation performance is insufficient for heat generated
during the operation. Therefore, the emission efficiency must be
reduced that much.
SUMMARY OF THE INVENTION
[0015] It is an object of the invention to provide a light emitting
element that has an increased emission area relative to the
element's surface area and prevents unevenness in light
distribution so as to increase brightness thereof.
[0016] It is a further object of the invention to provide a light
emitting element that has an excellent mounting performance, a high
reliability in electrical connection, and a heat radiation
performance as well as having an increased emission area relative
to the element's surface area.
[0017] It is a further object of the invention to provide a method
of making the light emitting element thus featured while using the
conventional apparatus without requiring any advance technique.
(1) According to one aspect of the invention, a light emitting
element comprises:
[0018] a semiconductor layer comprising a light-emitting layer;
[0019] a first electrode that is defined corresponding to the
light-emitting layer to supply power to the light-emitting
layer;
[0020] a second electrode that is defined as a counter electrode of
the first electrode;
[0021] an insulation layer than is formed on a mounting face side
of the semiconductor layer; and
[0022] a first terminal and a second terminal that are formed on a
surface of the insulation layer corresponding to the first
electrode and the second electrode, respectively,
[0023] wherein the first electrode and the second electrode are
formed on the mounting face side of the semiconductor layer,
[0024] the insulation layer comprises a first opening and a second
opening that are formed corresponding to the first electrode and
the second electrode, respectively, and
[0025] the first electrode and the second electrode are
electrically connected through the first hole and the second hole,
respectively, to the first terminal and the second terminal.
(2) According to another aspect of the invention, a light emitting
element comprises:
[0026] a semiconductor layer comprising a light-emitting layer;
[0027] a first electrode that is defined corresponding to the
light-emitting layer to supply power to the light-emitting
layer;
[0028] a second electrode that is defined as a counter electrode of
the first electrode;
[0029] wherein the first electrode and the second electrode are
formed on the mounting face side of the semiconductor layer,
and
[0030] the light-emitting layer and the first electrode are
surrounded by the second electrode
(3) According to another aspect of the invention, a light emitting
element comprises:
[0031] a semiconductor layer comprising a light-emitting layer;
and
[0032] an n-type electrode and a p-type electrode to supply power
to the light-emitting layer,
[0033] wherein the n-type electrode and the p-type electrode are
provided at a periphery of the semiconductor layer that has a width
smaller than an entire width of the light emitting element.
(4) According to another aspect of the invention, a method of
making a light emitting element comprises:
[0034] a semiconductor layer formation step of forming a
semiconductor layer comprising a light-emitting layer by stacking a
semiconductor material on a wafer underlying substrate;
[0035] a semiconductor layer removal step of partially removing the
semiconductor layer in a predetermined width and a predetermined
depth from a surface of the semiconductor layer to formed an
exposed portion;
[0036] an electrode formation step of forming electrodes to supply
power to an n-type layer and a p-type layer of the semiconductor
layer at the exposed portion; and
[0037] an element formation step of cutting the underlying
substrate with the semiconductor layer into a light emitting
element to allow the electrodes to be exposed to a periphery of the
light emitting element
(Advantages of the Invention)
[0038] In the invention, since the p-type and n-type electrodes can
be varied in arbitrary form, the light emitting element can have an
increased emission area relative to the element's surface area and
prevent unevenness in light distribution so as to increase
brightness thereof.
[0039] Further, the light emitting element can have an excellent
mounting performance, a high reliability in electrical connection,
and a heat radiation performance even in a large size type.
[0040] In addition, the method of making the light emitting element
can be conducted by using the conventional apparatus without
requiring any advance technique.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] The preferred embodiments according to the invention will be
explained below referring to the drawings, wherein:
[0042] FIG. 1A is a cross sectional view showing an LED element in
a first preferred embodiment according to the invention, where the
LED element is cut in a diagonal line thereof;
[0043] FIG. 1B is a top view showing the form of a p-electrode and
an n-electrode in the LED element in FIG. 1A;
[0044] FIG. 1C is a top view showing an insulation layer with an
opening in the LED element in FIG. 1A;
[0045] FIG. 1D is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 1A;
[0046] FIG. 2A is a cross sectional view showing an LED element in
a second preferred embodiment according to the invention, where the
LED element is cut in a diagonal line thereof;
[0047] FIG. 2B is a top view showing the form of a p-electrode and
an n-electrode in the LED element in FIG. 2A;
[0048] FIG. 2C is a top view showing an insulation layer with an
opening in the LED element in FIG. 2A;
[0049] FIG. 2D is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 2A;
[0050] FIG. 2E is a top view showing a modification of the
n-electrode in FIG. 2B;
[0051] FIGS. 3A to 3E are top views showing modifications of the
n-electrode and the p-electrode in the LED element of the second
embodiment;
[0052] FIG. 4A is a top view showing a modification of the
insulation layer in the LED element of the second embodiment;
[0053] FIG. 4B is a cross sectional view showing the insulation
layer in FIG. 4A;
[0054] FIG. 5A is a cross sectional view showing an LED element in
a third preferred embodiment according to the invention, where the
LED element is cut in a diagonal line thereof;
[0055] FIG. 5B is a top view showing the form of a p-electrode and
an n-electrode in the LED element in FIG. 5A;
[0056] FIG. 5C is a top view showing an insulation layer with an
opening in the LED element in FIG. 5A;
[0057] FIG. 5D is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 5A;
[0058] FIG. 6 is a cross sectional view showing an LED element in a
fourth preferred embodiment according to the invention;
[0059] FIG. 7A is a top view showing the form of a p-electrode is
and an n-electrode in a fifth preferred embodiment according to the
invention;
[0060] FIG. 7B is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 7A;
[0061] FIG. 9A is a top view showing the form of a p-electrode and
an n-electrode in a sixth preferred embodiment according to the
invention;
[0062] FIG. 8B is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 8A;
[0063] FIG. 9A is a top view showing the form of a p-electrode and
an n-electrode in a seventh preferred embodiment according to the
invention;
[0064] FIG. 9B is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 9A;
[0065] FIG. 10A is a top view showing the form of a p-electrode and
an n-electrode in an eighth preferred embodiment according to the
invention;
[0066] FIG. 10B is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 10A;
[0067] FIG. 11A is a top view showing the form of a p-electrode and
an n-electrode in a ninth preferred embodiment according to the
invention;
[0068] FIG. 11B is a top view showing a p-terminal portion and an
n-terminal portion in the LED element in FIG. 11A;
[0069] FIG. 12 is a perspective view showing the conventional LED
element;
[0070] FIG. 13A is a cross sectional view showing an LED element in
a tenth preferred embodiment according to the invention, where the
LED element is cut in a diagonal line thereof;
[0071] FIG. 13B is a top view showing the LED element in FIG. 13A,
where the LED element is view from the light extraction side;
[0072] FIGS. 14A to 14D are cross sectional views showing a process
of making the LED element of the tenth embodiment, where shown are
steps until when an insulation layer 116 is formed;
[0073] FIGS. 15A to 15C are cross sectional views showing a process
of making the LED element of the tenth embodiment, where shown are
steps from the formation of electrodes until the completion;
[0074] FIG. 16A is a cross sectional view showing a flip-chip
mounting example of the LED element of the tenth embodiment onto a
mounting board;
[0075] FIG. 16B is a cross sectional view showing a flip-chip
mounting example of the LED element of the tenth embodiment onto a
mounting board with a concave portion;
[0076] FIG. 17A is a top view showing an LED element in an eleventh
preferred embodiment according to the invention;
[0077] FIG. 17B is a cross sectional view cut along a line A-A in
FIG. 17A;
[0078] FIG. 17C is a top view showing the solder connection of the
LED element of the eleventh embodiment, which is viewed from the
side of a sapphire substrate thereof;
[0079] FIG. 18A is a top view showing an LED element in a twelfth
preferred embodiment according to the invention;
[0080] FIG. 18B is a cross sectional view cut along a line B-B in
FIG. 18A;
[0081] FIG. 19 is a cop view showing an LED element in a thirteenth
preferred embodiment according to the invention;
[0082] FIG. 20 is a top view showing an LED element in a fourteenth
preferred embodiment according to the invention;
[0083] FIG. 21 is a cross sectional view showing a mounting
structure of an LED element in a fifteenth preferred embodiment
according to the invention, where the LED element is connected to a
copper lead;
[0084] FIG. 22A is a cross sectional view showing a first mounting
structure of an LED element in a sixteenth preferred embodiment
according to the invention;
[0085] FIG. 22B is a cross sectional view showing a second mounting
structure of an LED element in the sixteenth embodiment according
to the invention;
[0086] FIG. 23 is a cross sectional view showing a mounting
structure of an LED element in a seventeenth preferred embodiment
according to the invention;
[0087] FIG. 24 is a cross sectional view showing a mounting
structure of an LED element in an eighteenth preferred embodiment
according to the invention;
[0088] FIG. 25A is a cross sectional view showing a large-size LED
element (1 mm square) in a nineteenth preferred embodiment
according to the invention; and
[0089] FIG. 25B is a top view showing the LED element in FIG. 25A,
which is viewed from the side of an insulation layer formation
surface thereof.
DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENTS
First Embodiment
(Composition of LED Element 1)
[0090] FIGS. 1A to 1D show an LED element in the first preferred
embodiment according to the invention.
[0091] The LED element 1 is composed of: a sapphire substrate 10;
an AlN buffer layer 11 formed on the sapphire substrate 10; an
n-GaN layer 12 formed on the AlN buffer layer 11; a light-emitting
layer 13 formed on the n-GaN layer 12; a p-GaN layer 14 formed on
the light-emitting layer 13, the n-GaN layer 12 to the p-GaN layer
14 being of group III nitride-based compound semiconductor; an
n-electrode 15 as a second electrode formed on part of the n-GaN
layer 12 exposed by partially etching the p-GaN layer 14 to the
n-GaN layer 12; a p-electrode 16 as a first electrode formed on the
p-GaN layer 14 to supply current to the light-emitting layer 13; an
insulation layer 17 of a SiO.sub.2-based material formed to cover
the electrode formation side; an n-terminal 18 electrically
connected through an opening 17n provided in the insulation layer
17 to the n-electrode 15; and a p-terminal 19 electrically
connected through an opening 17p provided in the insulation layer
17 to the p-electrode 16. The LED element 1 has a size of 0.3
mm.times.0.3 mm, which is widely prevalent.
[0092] A method of forming a group III nitride-based compound
semiconductor layer is not specifically limited, and well-known
metal organic chemical vapor deposition (MOCVD) method, molecular
beam epitaxy (MBE) method, hydride vapor phase epitaxy (HVPE)
method, sputtering method, ion plating method, cascade shower
method and the like are applicable.
[0093] The LED element may have a homostructure, a heterostructure,
or a double heterostructure. Furthermore, a quantum well structure
(a single quantum well structure or a multiquantum well structure)
is also applicable.
[0094] The p-electrode 16 is formed such that its surface occupies
60% or more of the surface of the LED element 1.
(Method of Making the LED Element 1)
[0095] The method of making the LED element 1 will be explained
below.
(Step of Providing the Substrate)
[0096] First, a wafer sapphire substrate 10 is provided as an
underlying substrate.
(Step of Forming the Semiconductor Layers)
[0097] Then, the AlN buffer layer 11 is formed on a surface of the
sapphire substrate 10. Then, the n-GaN layer 12, the light emitting
layer 13, and the p-GaN layer 14 are sequentially formed on the AlN
buffer layer 11. Then, a stack portion from the p-GaN layer 14 to
the n-GaN layer 12 is partially removed by etching to expose the
n-GaN layer 12. The etching is conducted such that the p-GaN layer
14 has a sufficient surface area relative to the surface of the LED
element 1.
(Step of Forming the Electrodes)
[0098] Then, as shown in FIG. 1B, the n-electrode 15 and the
p-electrode 16 of Au are formed by deposition on the exposed
surface of the n-GaN layer 12 and the surface of the p-GaN layer
14, respectively. Alternatively, the n-electrode 15 and the
p-electrode 16 may be formed by other film formation method suas as
sputtering.
(Step of Forming the Insulation Layer)
[0099] Then, as shown in FIG. 1C, the insulation layer 17 of the
SiO.sub.2-based material is formed to cover the electrode formation
side. Then, a mask pattern corresponding to the openings 17n and
17p is formed on the insulation layer 17 and then etched to form
the openings 17n and 17p in the insulation layer 17
(Step of Forming the Terminals)
[0100] Then, as shown in FIG. 1D the n-terminal 18 and the
p-terminal 19 of Au are formed by deposition at the corresponding
openings 17n and 17p in the insulation layer 17 Although in FIG. 1D
the n-terminal 18 is shown smaller than the p-terminal 19, the
n-terminal 18 and the p-terminal 19 can be formed in arbitrary form
within a size not to be short-circuited each other since the
electrode formation surface of the LED element 1 is covered with
the insulation layer 17.
[0101] In making an LED lamp by using the LED element 1 thus
fabricated, for example, a substrate of ceramics material is
provided, on the surface of which a wiring pattern of copper foil
is formed. The LED element 1 is positioned on the wiring pattern of
the substrate and flip-chip mounted by the reflowing of solder.
Then, it is integrally sealed with a seal material such as epoxy
resin and glass material to have the packaged LED lamp.
(Operation of the LED Element 1)
[0102] When the LED lamp thus made is supplied with power by
connecting the wiring pattern on the substrate to a power supply
(not shown), a forward voltage is applied through the n-terminal 18
and the p-terminal 19 to the n-electrode 15 and the p-electrode 16.
Thereby, radiative recombination of hole and electron occurs in the
light-emitting layer 13 and blue light is emitted according to the
form of the p-electrode 16 as shown in FIG. 1B. Blue light
irradiated to the n-GaN layer 12 side is externally radiated
passing through the sapphire substrate 10. Blue light irradiated to
the p-GaN layer 14 side is reflected on the p-electrode 16 back to
the light-emitting layer 13 and externally radiated passing through
the sapphire substrate 10 as well
(Effects of the First Embodiment)
[0103] The effects of the first embodiment are as follows. [0104]
(1) Since the LED element 1 is at the electrode formation surface
provided with the n-terminal 18 and the p-terminal 19 of Au to have
an external connection through the insulation layer 17, the
n-electrode 15 and the p-electrode 16 can be formed in arbitrary
form without being limited to an electrode form needed to secure
the mounting property of the LED element 1. Thus, the p-electrode
16 can be designed considering the emission form and thereby the
emission area can be increased. Therefore, even when current is
supplied according to an increase in the emission area, the current
density in the light-emitting layer can be kept equal. As a result,
the amount of emitted light can be increased. [0105] (2) In the
conventional LED element, since there was a large nonradiative
portion in area ratio, symmetry in emission must be significantly
broken. However, in the first embodiment, since the nonradiative
area is reduced relative to the emission area of the LED element,
blue light can be uniformly radiated from the entire emission
surface of the LED element 1 without unevenness in light
distribution. [0106] (3) Since the emission surface area is
increased relative to the emission area of the LED element, the
current density in the light-emitting layer can be reduced even in
the same current supply as the conventional LED element. Therefore,
the thermal localization in the LED element 1 can be prevented.
Thereby, the emission efficiency can be kept even when it is used
for long hours. [0107] (4) Since the irregularity in emission form
can be prevented, when it is used for an LED lamp with a converging
optical system, the convergence performance can be enhanced without
deforming the image of light source projected and therefore a
natural emission pattern can be obtained. [0108] (5) The n-terminal
18 and the p-terminal 19 can be formed with a size and a distance
not dependent on the size of the n-electrode 15 and the p-electrode
16, Therefore, it can be mounted by the reflowing of solder. Thus,
the performance in mounting and heat radiation can be enhanced.
[0109] In the first embodiment, the electrical bonding to the
n-terminal 18 and the p-terminal 19 can be conducted using Au bumps
when the LED element 1 is mounted.
[0110] The composition of the LED element 1 is not limited to the
blue LED element of group III nitride-based compound semiconductor.
The LED element may emit light in other emission color and may be
of another material.
[0111] Although in the first embodiment the LED element 1 is 0.3
mm.times.0.3 mm in size, it can be 0.2 mm.times.0.2 mm or smaller
in size while securing an emission area. Thus, the LED element 1
can be realized in a size never before developed due to the
limitation of the n-electrode area.
[0112] Also, the LED element 1 can have an elongated size such as
0.1 mm.times.0.3 mm for a practical use. The LED element 1 thus
formed can increase a coupling efficiency to a thin-type light
guiding plate.
Second Embodiment
(Composition of LED Element 1)
[0113] FIGS. 2A to 2D show an LED element in the second preferred
embodiment according to the invention.
[0114] Herein, like components are indicated by the same numerals
as used in the first embodiment.
[0115] The flip-chip type LED element 1 is different from the first
embodiment in that, as shown in FIG. 2A, the p-GaN layer 14 is
disposed like an island at the center of the LED element 1, the
p-electrode 16 is formed thereon, and the n-electrode 15 is
disposed circularly around the p-electrode 16.
[0116] The n-electrode 15 is about 10 .mu.m in line width of
narrowest portion and about 350 .mu.m in line width of widest
portion. The p-electrode 16 is, as shown in FIG. 2B, shaped like a
square with rounded corners, and a predetermined distance separated
through an insulation portion 100 from the n-electrode 15 which
circularly surrounds the p-electrode 16. The predetermined distance
is preferably such a minimum one that can prevent the light leakage
from the GaN layer and the short-circuiting.
[0117] The insulation layer 17 is, as shown in FIG. 2C, formed
depending on the disposition of the n-electrode 15 and the
p-electrode 16. Although in FIG. 2C, the n-electrode 15 and the
p-electrode 16 are disposed diagonally at the bottom of the LED
element 1, they may be in parallel disposed a predetermined
distance separated each other.
[0118] The n-terminal 18 and the p-terminal 19 are, as shown in
FIG. 2D, disposed to cover the openings 17n, 17P. Thereby, they are
electrically connected to the n-electrode 15 and the p-electrode 16
(though not shown in FIG. 2D) covered by the insulation layer
17.
Effects of the Second Embodiment
[0119] The effects of the second embodiment are as follows. [0120]
(1) The p-GaN layer 14 is disposed like an island at the center of
the LED element 1, the p-electrode 16 is formed thereon, and the
n-electrode 15 is disposed circularly around the p-electrode 16.
Thus, the emission portion can be disposed at the center of the LED
element 1. Since electros are uniformly supplied from all regions
of the p-GaN layer 14, a uniform emission can be generated in the
light-emitting layer 33 under the p-electrode 16. Therefore,
uniform blue light can be externally radiated from the LED element
1 to reduce unevenness in light distribution. [0121] (2) Since the
n-electrode 15 is circularly disposed around the p-electrode 16,
heat of the n-electrode 15 can be dispersed widely to the LED
element 1 to stabilize the light output characteristics. Further,
due to the enhancement in thermal dispersion property, the heat
radiation property can be improved to prevent the overheating of
the LED element 1. [0122] (3) Since the light-emitting layer 13 is
formed symmetrical, a natural emission pattern can be obtained even
when the LED element 1 is used in combination with the convergence
optical system.
[0123] Meanwhile, as shown in FIG. 2E, the n-electrode 15 is not
always formed perfectly around the p-electrode 16. When it is
formed substantially around the p-electrode 16, the same effects
can be obtained.
[0124] FIGS. 3A to 3E are top views showing modifications of the
n-electrode and the p-electrode in the LED element of the second
embodiment.
(Modification 1 of Electrode Form)
[0125] As shown in FIG. 3A, the n-electrode 15 may have a
separation portion 150 that diagonally separates the p-electrode
16.
[0126] In modification 1, since the formation region of the
p-electrode 16 is separated into two parts, current can be
uniformly and rapidly spread and thereby good emission
characteristics can be obtained under the p-electrode 16
(Modification 2 of Electrode Form)
[0127] As shown in FIG. 3B, the n-electrode 15 may have a cross
portion 151 at the center of the separation portion 150.
[0128] In modification 2, since the cross portion 151 is formed
while the formation region of the p-electrode 16 is separated into
two parts by the separation portion 150, current can be further
uniformly and rapidly spread and thereby good emission
characteristics can be obtained under the p-electrode 16.
(Modification 3 of Electrode Form)
[0129] As shown in FIG. 3C, a p-electrode 16A may be formed at the
center of the surface of the LED element 1 surrounded by the
n-electrode 15 and a p-electrode 16B may be formed around the
n-electrode 15.
[0130] FIG. 3D shows the n-terminal 18 and the p-terminal 19 formed
on the insulation layer 17. The insulation layer 17 is formed on
the surface of the n-electrode 15 and the p-electrodes 16A, 16B as
shown in FIG. 3C while having the openings 17n, 17p. The n-terminal
18 and the p-terminal 19 are formed triangular in surface form
while being partially embedded in the openings 17n, 17p. The
p-terminal 19 is embedded in the two openings 17p, 17p and thereby
electrically connected to the p-electrodes 16A, 16B.
[0131] In modification 3, since the p-electrodes 16A, 16B are
disposed inside and outside of the n-electrode 15, a good current
spreading property can be obtained to allow the good emission
characteristics of the LED element 1 while reducing the area of the
n-electrode 15.
(Modification 4 of Electrode Form)
[0132] As shown in FIG. 3E, the n-electrode 15 may have a triangle
portion 153 formed at a corner of the surface of the LED element 1
while the n-electrode 15 has the cross portion 151 in the region of
the p-electrode 16 to connect the triangle portion 153.
[0133] In modification 4, since the n-electrode 15 has the cross
portion 151 and the triangle portion 153 in the region of the
p-electrode 16 without surrounding the p-electrode 16, the
p-electrode 16 can have an increased area. Thereby, the emission
characteristics can be enhanced while preventing unevenness in
light distribution.
(Modification of the Insulation Layer 17)
[0134] FIGS. 4A and 4B show a modification of the insulation layer
17.
[0135] A modified insulation layer 170 is composed of a first
insulation layer 171, a second insulation layer 172, and a
reflection layer 173 formed sandwiched by the first and the second
insulation layers 171 and 172. The reflection layer 173 is made of
aluminum (Al) by deposition. The insulation layer 170 is provided
with openings 17n, 17P to connect the underlying n-electrode 15 and
p-electrode 16 with the n-terminal and the p-terminal 19 (not
shown).
[0136] Except the openings 17n, 17P, the reflection layer 173 is
formed as shown in FIG. 4B. Thereby, light can be prevented from
leaking in the opposite direction of the substrate through a gap
between the n-electrode 15 and the p-electrode 16.
[0137] The reflection layer 173 may be made of silver (Ag) or
rhodium (Rh) instead of aluminum (Al).
[0138] In this modification, since the leakage of light through the
gap between the electrodes can be prevented, the brightness of the
LED element 1 can be enhanced even when the n-electrode 15 is
formed in the region of the p-electrode 16.
[0139] Although a bonding pad conventionally needs to have a
bonding area of about .phi.100 .mu.m, it may be a pattern (in
arbitrary form) narrower than this area. Especially, it is
effective that it has a line width of 50 .mu.m or less, further 25
.mu.m or less, This is because the bonding pad needed to bond a
wire or bump affects on current supplied to the LED element 1. In
general, a wire of .phi.25 .mu.m or so is used and the bonding pad
therefor needs an area twice the wire diameter. It is not effective
that the bonding area is smaller than the wire diameter.
[0140] In the invention, if the n-electrode 15 is in line width
narrower than the bonding pad needed conventionally as mentioned
above, the effects abovementioned can be obtained. Although the
n-electrode 15 is generally a narrow line of 50 .mu.m or less, it
is not limited to this size in a large current LED and may be a
narrow line with a width narrower than the corresponding bonding
pad.
[0141] Further, since the same effects can be obtained by
substantially surrounding the p-electrode 16 as shown in FIG. 2E,
the n-electrode 15 is not always formed perfectly around the
p-electrode 16.
[0142] If the improvement of light distribution is desired
primarily, the light-emitting layer 13 may be formed circular etc.
In this case, there is a certain space at the diagonal position of
the surface of the LED element 1. Therefore, the n-electrode 15 is
not always formed a narrow line pattern and the terminal may be
formed without forming the insulation layer 17.
Third Embodiment
(Composition of LED Element 1)
[0143] FIGS. 5A to 5D show an LED element in the third preferred
embodiment according to the invention.
[0144] The flip-chip type LED element 1 is different from the first
embodiment in that, as shown in FIG. 5A, the p-GaN layer 14 is
disposed like an island at the center of the LED element 1, the
p-electrode 16 is formed thereon, the n-electrode 15 is disposed
circularly around the p-electrode 16, and the p-GaN layer 14 is
provided with an uneven sidewall 14A formed uneven at the side
thereof.
[0145] The uneven sidewall 14A is formed by partially removing the
p-GaN layer 14 to the n-GaN layer 12 by etching to expose the n-GaN
layer 12. It may be formed by another process such as cutting.
Effects of the Third Embodiment
[0146] In the third embodiment, since the p-GaN layer 14 is formed
like an island at the center of the LED element 1 and the uneven
sidewall 14A is formed around the p-GaN layer 14, in addition to
the effects of the second embodiment, it is easy to extract light
(herein called intra-layer confined light) confined in the
light-emitting layer 13. Thus, the external radiation efficiency
can be enhanced.
[0147] Although in FIGS. 5B to 5D the uneven surface is illustrated
with exaggeration, it is desirable that a fine uneven surface is
made to secure a larger surface area of the p-GaN layer 14. Thus,
the fineness of the uneven surface may be in the range of an
emission wavelength and an optimum design in light extraction can
be made according to a refractive index of the material, the layer
composition etc.
Fourth Embodiment
(Composition of LED Element 1)
[0148] FIG. 6 is a cross sectional view showing an LED element in
the fourth preferred embodiment according to the invention.
[0149] The flip-chip type LED element 1 is different from the
second embodiment in that a GaN substrate 20 is used in place of
the sapphire substrate 10 and is provided with cut portions 20A
being 45 degrees cut off at the corner of the light extraction
surface of the LED element 1.
Effects of the Fourth Embodiment
[0150] In the fourth embodiment, since the GaN substrate 20 is used
as an underlying substrate, the group III nitride-based compound
semiconductor layer has a refractive index equal to the GaN
substrate 20. Therefore, blue light emitted from the light-emitting
layer 13 can reach the light extraction surface of the GaN
substrate 20 instead of being totally reflected on the interface of
the group III nitride-based compound semiconductor layer and the
GaN substrate 20. Further, since the GaN substrate 20 is provided
with the cut portions 20A at the corner of the light extraction
surface, the light extraction efficiency can be enhanced to
efficiently extract blue light.
Fifth Embodiment
(Composition of LED Element 1)
[0151] FIGS. 7A and 7B show an LED element in the fifth preferred
embodiment according to the invention.
[0152] The flip-chip type LED element 1 is formed a large size (1
mm.times.1 mm), and as shown in FIG. 7A it is composed of the
p-electrodes 16 formed rectangular and disposed in parallel and the
n-electrode 15 formed to surround the p-electrodes 16 Further, as
shown in FIG. 7B, the insulation layer 17 is provided with an
opening 17n formed linearly therein corresponding to the
n-electrode 15 and multiple openings 17p formed circular therein
corresponding to the p-electrode 16. The n-electrode 15 and the
p-electrode 16 are electrically connected through the openings 17n,
17p to the n-terminal 18 and the p-terminal 19, respectively.
[0153] As shown in FIG. 7B, the n-terminal 18 and the p-terminal 19
are formed rectangular in a predetermined width while being
disposed along the opposite sides of the LED element 1.
Effects of the Fifth Embodiment
[0154] In the fifth embodiment, since the emission area is
increased relative to the surface area of the LED element 1 in the
large size LED 1, the brightness can be enhanced without reducing
the heat radiation property.
[0155] The LED element 1 can be mounted through a solder other than
Au. In using the solder, since a surface heat radiation path is
formed through the solder, unevenness in temperature can be
prevented in the LED element 1.
[0156] Due to the large size, the design freedom of electrode
formation can be enhanced.
[0157] Further, the productivity can be enhanced since the
p-electrode 16 and the n-electrode 15 have the rectangular shape
easy to form.
[0158] In the fifth embodiment, by using the insulation layer 170
as explained earlier instead of the insulation layer 17, light can
be prevented from leaking through a gap between the n-electrode 15
and the p-electrode 16. Thereby, the brightness can be further
enhanced.
Sixth Embodiment
(Composition of LED Element 1)
[0159] FIGS. 8A and 8B show an LED element in the sixth preferred
embodiment according to the invention.
[0160] The flip-chip type LED element 1 is formed a large size (1
mm.times.1 mm), and as shown in FIG. 8A it has an electrode form
that the formation area of the p-electrode 16 is arranged like a
zigzag to the formation area of the n-electrode 15. Further, as
shown in FIG. 8B, the insulation layer 17 is provided with openings
17n, 17p, through which the n-electrode 15 and the p-electrode 16
are electrically connected to the n-terminal 18 and the p-terminal
19, respectively.
[0161] The n-terminal 18 and the p-terminal 19 are diagonally
disposed at the corner of the LED element 1, and a heat radiation
layer 25 of Rh--Au is formed a thin film therebetween.
Effects of the Sixth Embodiment
[0162] In the sixth embodiment, like the fifth embodiment, the
emission area can be increased relative to the surface of the LED
element 1. Further, since the heat radiation layer 25 with a good
heat radiation property is formed on the surface of the is
insulation layer 17, the LED element 1 can be stably operated even
in large current or long operation. Since the heat radiation layer
25 can reflect light leaked through a gap between the n-electrode
15 and the p-electrode 16, loss of emitted light can be
reduced.
[0163] In place of the insulation layer 17, the insulation layer
170 as explained earlier may be used. Thereby, light can be
prevented from leaking through a gap between the heat radiation
layer and the n-electrode 15 or the p-electrode 16. Thereby, the
brightness can be further enhanced.
Seventh Embodiment
(Composition of LED Element 1)
[0164] FIGS. 9A and 9B show an LED element in the seventh preferred
embodiment according to the invention.
[0165] The flip-chip type LED element 1 is formed a large size (1
mm.times.1 mm), and as shown in FIG. 9A it has an electrode form
that the multiple p-electrodes 16 are formed hexagonal or
semi-hexagonal and arranged zigzag and the n-electrode 15 is formed
around the p-electrode 16. Further, as shown in FIG. 9B, the
insulation layer 17 is provided with openings 17n (in trident
form), 17p (in circular form), through which the n-electrode 15 and
the p-electrode 16 are electrically connected to the n-terminal 18
and the p-terminal 19, respectively.
Effects of the Seventh Embodiment
[0166] In the seventh embodiment, since the hexagonal emission
region is formed by the electrode form with the hexagonal
p-electrode 16 surrounded by the n-electrode 15, the light-emitting
layer 13 under the p-electrode 16 can have a high emission
intensity. Further, due to the integration of the emission regions
with a high emission intensity, the brightness can be enhanced at
the entire surface of the LED element 1.
Eighth Embodiment
(Composition of LED Element 1)
[0167] FIGS. 10A and 10B show an LED element in the eighth
preferred embodiment according to the invention.
[0168] The flip-chip type LED element 1 is formed a large size (1
mm.times.1 mm), and as shown in FIG. 10A it has an electrode form
that the cross-shaped n-electrode 15 is formed in the formation
area of the p-electrode 16. Further, as shown in FIG. 10B, the
insulation layer 17 is provided with openings 17n, 17p, through
which the n-electrode 15 and the p-electrode 16 are electrically
connected to the n-terminal 18 and the p-terminal 19,
respectively.
[0169] The p-terminal 19 is formed such that its surface area is
increased relative to the surface of the LED element 1 to enhance
the radiation of heat generated in operating the LED element 1.
Also, it is formed to cover most of the n-electrode 15 since the
n-electrode 15 generates relatively much heat.
Effects of the Eighth Embodiment
[0170] In the eighth embodiment, since the surface area of the
p-electrode 16 is relatively increased by disposing the
cross-shaped n-electrode 15 in the formation area of the
p-electrode 16, unevenness in temperature can be prevented in the
LED element 1. Further, unevenness in light distribution can be
reduced, design freedom in electrode formation can be enhanced, and
the brightness can be enhanced.
Ninth Embodiment
(Composition of LED Element 1)
[0171] FIGS. 11A and 11B show an LED element in the ninth preferred
embodiment according to the invention.
[0172] The flip-chip type LED element 1 is formed a large size (1
mm.times.1 mm)), and as shown in FIG. 11A it has an electrode form
that an inverted E-shaped n-electrode 15 is formed in the formation
area of the p-electrode 16, a linear n-electrode 15 is formed
outside of the p-electrode 16, and the inverted E-shaped
n-electrode 15 is connected to the linear n-electrode 15. Further,
as shown in FIG. 11B, the insulation layer 17 is provided with
openings 17n (in leaner form), 17p (in circular form), through
which the n-electrode 15 and the p-electrode 16 are electrically
connected to the n-terminal 18 and the p-terminal 19,
respectively.
[0173] The n-terminal 18 is formed to cover the formation area of
the n-electrode 15 so as to reflect light leaked through a gap
between the n-electrode 15 and the p-electrode 16 back to the
semiconductor layer side.
Effects of the Ninth Embodiment
[0174] In the ninth embodiment, the emission area can be increased
relative to the surface of the LED element 1. Further, a good
emission property can be obtained while reducing the relative area
of the n-electrode 15 to the p-electrode 16.
[0175] Also in the ninth embodiment, in place of the insulation
layer 17, the insulation layer 170 as explained earlier may be
used. Thereby, light can be prevented from leaking through a gap
between the heat radiation layer and the n-electrode 15 or the
p-electrode 16. Thereby, the brightness can be further
enhanced.
[0176] Since the resistivity of a p-layer is high in GaN-based
semiconductors, the emission area is located substantially under or
over a p-electrode. Therefore, the electrode formed as descried
above is particularly effective. Alternatively, the electrode
formation may be used for another semiconductor material. In this
case, the electrode pattern may be reversed depending on the level
of resistivity.
Tenth Embodiment
(Composition of LED Element 1)
[0177] FIGS. 13A and 13B show an LED element in the tenth preferred
embodiment according to the invention.
[0178] As shown in FIG. 13A, the LED element 101 is composed of: a
sapphire substrate 110; an AlN buffer layer 111 formed on the
sapphire substrate 110; an n-GaN layer 112 formed on the AlN buffer
layer 111; a light-emitting layer 113 formed on the n-GaN layer
112; a p-GaN layer 114 formed on the light-emitting layer 113, the
n-GaN layer 112 to the p-GaN layer 114 being of group III
nitride-based compound semiconductor and composing a GaN-based
semiconductor layer 200; a p-contact electrode 115 formed on the
p-GaN layer 114 to spread current into the p-GaN layer 114; a
transparent insulation layer 116 formed on the side of the
GaN-based semiconductor layer 200 and on the p-contact electrode
115, an n-external electrode 117 formed on part of the n-GaN layer
112 exposed by partially etching the p-GaN layer 114 to the n-GaN
layer 112 and on the side of the insulation layer 116; a p-external
electrode 118 formed on the side of the insulation layer 116 in
contact with the p-contact electrode 115; and a transparent
insulation layer 119 formed to cover the element surface between
the n-external electrode 117 and the p-external electrode 118.
[0179] Herein, the GaN-based semiconductor layer 200 comprises a
stack portion from the n-GaN layer 112 to the p-GaN layer 114.
Light emitted from the light-emitting layer 113 of the LED element
101 has an emission wavelength of 460 nm.
[0180] A method of forming a group III nitride-based compound
semiconductor layer is not specifically limited, and well-known
metal organic chemical vapor deposition (MOCVD) method, molecular
beam epitaxy (MBE) method, hydride vapor phase epitaxy (HVPE)
method, sputtering method, ion plating method, cascade shower
method and the like are applicable.
[0181] The LED element may have a homostructure, a heterostructure,
or a double heterostructure. Furthermore, a quantum well structure
(a single quantum well structure or a multiquantum well structure)
is also applicable.
[0182] The p-contact electrode 115 serves to spread current into
the p-GaN layer 114 and to give a good electrical connection with
an external member or device. It is made of rhodium (Rh) with a
light reflection property. The p-contact electrode 115 may be made
of transparent ITO (indium tin oxide) or ZnO or a transparent
material such as Au/Co, Ni/Ti if it can be in ohmic contact with
the p-GaN layer 114.
[0183] The insulation layer 116 is made of SiO.sub.2 and disposed
to cover the side of the GaN-based semiconductor layer 200 to
prevent the short-circuiting of the n-external electrode 117 and
the p-external electrode 118 with the GaN-based semiconductor layer
200. It may be made of another insulative material such as SiN
instead of SiO.sub.2.
[0184] The n-external electrode 117 is made of V/Al, and the
p-external electrode 118 is made of Ti. These external electrodes
are formed such that they are exposed on an element periphery
ranging from the side of the element to an edge of the surface of
the insulation layer 119 so as to allow the electrical bonding at
the side of the element and the surface mounting at the surface
side of the p-contact electrode 115. Herein, the element periphery
comprises the side of the LED element 101 and an edge of the
surface of the insulation layer 119 as shown in FIG. 13A. As shown
in FIG. 13B, the n-external electrode 117 ranges over the entire
length of two adjacent sides and the p-external electrode 118 is
formed part of two sides opposed to the two sides of the n-external
electrode 117. The p-external electrode 118 has a formation region
smaller than the n-external electrode 117. The electrode surface
may be solder-plated.
(Method of Making the LED Element 101)
[0185] FIGS. 14A to 14D are cross sectional views showing a process
of making the LED element of the tenth embodiment, where shown are
steps until when the insulation layer 116 is formed at the side of
the LED element 101.
[0186] Hereinafter, for the sake of explanation, only part of a
wafer corresponding to the LED element 101 is illustrated in the
drawings although, in fact, the wafer sapphire substrate 110 is
used to grow the semiconductor layer thereon and then the wafer
with the semiconductor layer is diced to obtain the LED element
101.
(Step of Forming the GaN-based Semiconductor Layer 200)
[0187] At first, as shown in FIG. 14A, the AlN buffer layer 111,
the GaN-based semiconductor layer 200 and the p-contact electrode
115 are formed on the wafer sapphire substrate 110 by MOCVD.
(First Etching Step)
[0188] Then, as shown in FIG. 14B, the GaN-based semiconductor
layer 200 is dry-etched to remove a stack portion from the surface
of the GaN-based semiconductor layer 200 to the n-GaN layer 112,
where the stack portion corresponds to a region to form the
n-external electrode 117 and the p-external electrode 118. Thereby,
an exposed portion 112A is formed at the side of the GaN-based
semiconductor layer 200. Alternatively, the p-contact electrode 115
may be formed placing a photoresist on the semiconductor layer
after the exposed portion 112A is formed, and then the photoresist
can removed
(Step of Forming the Insulation Layer 116)
[0189] Then, as shown in FIG. 14C, the insulation layer 116 is
formed by deposition on the GaN-based semiconductor layer 200 after
the dry etching.
(Second Etching Step)
[0190] Then, as shown in FIG. 14D, a photoresist is placed on the
GaN-based semiconductor layer 200 with the insulation layer 116
formed thereon, and then the insulation layer 116 is partially
etched except its portion corresponding to the side of the
GaN-based semiconductor layer 200. Thereby, part of the exposed
portion 112A and the p-contact electrode 115 are exposed.
[0191] FIGS. 15A to 15C are cross sectional views showing a process
of making the LED element of the tenth embodiment, where shown are
steps from the formation of electrodes until the completion.
(Step of Forming the External Electrodes 117, 118)
[0192] As shown in FIG. 15A, in the electrode formation process,
the n-external electrode 117 of V/Al is formed by deposition at the
exposed portion 112A on the n-external electrode 117 side. Then,
the p-external electrode 118 of Ti is formed by deposition at the
exposed portion 112A on the p-external electrode 118 side.
[0193] The n-external electrode 117 may be made of a material that
can be in ohmic contact with the n-GaN layer 112, for example, it
may be of Ti other than V/Al. The p-external electrode 118 may be
made of a material that can be electrically connected with the
p-contact electrode 115, for example, it may be of Al other than
Ti.
[0194] Further, both of the n-external electrode 117 and the
p-external electrode 118 may be of Ti. In this case, the n-external
electrode 117 and the p-external electrode 116 can be formed
together in the same step and thus the manufacturing step can be
simplified.
(Step of Forming the Insulation Layer 119)
[0195] Then, as shown in FIG. 5B, the insulation layer 119 of
SiO.sub.2 is formed by deposition over the upper surface of the
GaN-based semiconductor layer 200 including the electrode 115 and
the formation region of the n-external electrode 117 and the
p-external electrode 118.
(Third Etching Step)
[0196] Then, as shown in FIG. 15C, the insulation layer 119 is
etched placing a photoresist on the GaN-based semiconductor layer
200 and then the photoresist is removed. Thereby, the insulation
layer 119 is left except part on the n-external electrode 117 and
the p-external electrode 118 at the element periphery such that it
can prevent the short-circuiting of the n-external electrode 117
and the p-external electrode 118 and protect them.
(Dicing Step)
[0197] Then, the wafer composed of the GaN-based semiconductor
layer 200 with the n-external electrode 117 and the p-external
electrode 118 formed thereon and the sapphire substrate 110 is cut
into a given element size by a dicer (not shown). As a result, the
LED element 101 as shown in FIG. 15C can be obtained. The cutting
of the wafer can be conducted by another process such as scribing
instead of the dicing.
(Mounting of the LED Element 101)
[0198] FIG. 16A is a cross sectional view showing a flip-chip
mounting example of the LED element of the tenth embodiment onto a
mounting board.
[0199] As shown in FIG. 16A, the LED element 101 fabricated as
described above is mounted being bonded through an epoxy insulative
adhesive 141 onto the surface of a ceramics board 123 with a wiring
pattern 122 formed thereon. The n-external electrode 117 and the
p-external electrode 118 are reflow-bonded to the wiring pattern
122 through a solder 120A.
[0200] The insulative adhesive 141 may be of another material if it
has a good thermal conductivity, for example, it may a paste with
no adhesivity such that the LED element 101 can be in close contact
with the board 123 in sheet form. It is more desirable that 141 is
made of a material with high heat resistance and good
adhesivity.
[0201] If the insulation to the wiring pattern 122 can be secured,
the board 123 may be a conductive board that a metal material such
as Cu and Al with a high heat conductivity is subjected to
insulation treatment, instead of the abovementioned insulative
board such as a flexible board of ceramics, glass epoxy, polyimide
and conductive foil.
[0202] If no short-circuiting of the n-external electrode 117 and
the p-external electrode 118 is generated, the insulative adhesive
141 may be replaced by a conductive material to bond the LED
element 101 onto the board 123. Such a material can be a conductive
paste of silicone resin containing a filler such as Au, Cu and
Al.
[0203] The solder 120A may be replaced by a conductive adhesive
such as an epoxy resin containing Ag paste or a conductive filler
such as Au, Cu and Al so as to allow the electrical connection of
the n-external electrode 117 and the p-external electrode 118 with
the wiring pattern 122.
[0204] FIG. 16B is a cross sectional view showing a flip-chip
mounting example of the LED element of the tenth embodiment onto a
mounting board with a concave portion.
[0205] As shown in FIG. 16B, a board 123 with the concave portion
123A for positioning the element may be used such that part of the
p-contact electrode 115 is inserted into the concave portion 123A.
The concave portion 123A is coated with the insulative adhesive 141
to allow the bonding of the part of the p-contact electrode 115 of
the LED element 101. Like the manner as shown in FIG. 16A, the
n-external electrode 117 and the p-external electrode 118 are
reflow-bonded to the wiring pattern 122 through the solder
120A.
(Operation of the LED Element 101)
[0206] When power is supplied connecting the wiring pattern 122 on
the substrate to a power supply (not shown), a forward voltage is
applied through the n-external electrode 117 and the p-external
electrode 118 of the LED element 101 to the light-emitting layer
113. Thereby, radiative recombination of hole and electron occurs
in the light-emitting layer 113 and blue light is emitted. Blue
light irradiated to the sapphire substrate 110 side is externally
radiated passing through the sapphire substrate 110. Heat generated
during the operation of the LED element 101 is radiated through the
insulative adhesive 141 to the board 123.
Effects of the Tenth Embodiment
[0207] The effects of the tenth embodiment are as follows. [0208]
(1) Since the LED element 101 is fabricated with the n-external
electrode 117 and the p-external electrode 118 formed around the
light-emitting layer 113 based on the manufacturing process for the
semiconductor LED by using the wafer sapphire substrate 110, the
LED element 101 can be easily made in a lot and in mass production
by using the known apparatus and method. [0209] (2) Since the
n-external electrode 117 and the p-external electrode 118 are
formed around the light-emitting layer 113, not on the light
extraction surface, while partially removing the sides of the
GaN-based semiconductor layer 200, light emitted from the
light-emitting layer 113 can be prevented from being blocked by the
n-external electrode 117 and the p-external electrode 118. Further,
due to the disposition of the external electrodes, the emission
area of the light-emitting layer 113 can be increased in the same
element size and the emission intensity can be enhanced. Thus, the
LED element 101 can have a good light extraction efficiency and a
high brightness. [0210] (3) The electrical connection with the
wiring pattern 122 etc. can be made in any of flip-chip mounting or
face-up mounting. Namely, the type of mounting can be chosen
according to use. For example, another type of mounting other than
the above types can be conducted in which one side of the LED
element 101 is used in electrical or mechanical bonding. Thus,
various types of mounting can be offered. [0211] (4) Since the
nonradiative portion such as a wire bonding space and an
n-electrode bump space can be eliminated or reduced, even the small
size LED element 101 can have a sufficient ratio of emission
area/LED surface area. Therefore, a further small LED element 101
can be realized which has an electrode interval near to the element
width. For example, even an LED element 101 of 0.1 mm square can
have a practical emission area. If n-and p-electrodes for Au stud
bump mounting are disposed under the LED element 101, an electrode
with a diameter of about 0.1 mm needs to be provided
correspondingly. Thus, it is difficult to make an LED element 101
of less than 0.1.times.0.2 mm.sup.2. [0212] (5) Since the
n-external electrode 117 and the p-external electrode 118 are
continuously formed over the two sides of the element, the bonding
area of the solder 120A for reflow bonding can be increased,
thereby offering a stable mounting and a good heat radiation
property. Further, the secure mounting can be obtained without
requiring a high precision in positioning like the bump bonding.
Meanwhile, the n-external electrode 117 and the p-external
electrode 118 are not always continuously formed over the two
sides, and they may be formed not continuously. [0213] (6) In the
flip-chip bonding of the LED element 101, the surface of the
GaN-based semiconductor layer 200 is face-bonded to the board 123,
and the n-external electrode 117 and the p-external electrode 118
are electrically connected through the solder 120A. Therefore, the
bonding strength can be enhanced. The heat radiation property can
be improved such that heat is radiated from the GaN-based
semiconductor layer 200 to the board 123 without passing through
the sapphire substrate 110. Further, the reliability can be
improved such that the seal resin does not exist at the bonding
interface of the LED element 101 and, therefore, the separation of
bonded portion does not occur due to thermal expansion.
[0214] Although in the tenth embodiment the blue LED element 101 of
the group III nitride-based compound semiconductor is explained,
the invention is not limited to the blue LED element 101 and may be
applied to another emission color LED. Further, the LED element 101
may be made of another material instead of the group III
nitride-based compound semiconductor.
[0215] Alternatively, a GaN substrate may be used in place of the
sapphire substrate 110 as an underlying substrate to grow a group
III nitride-based compound semiconductor layer thereon.
[0216] Even when the LED element 101 is flip-chip mounted using the
p-contact electrode 115 as the mounting face as shown in FIG. 16A,
light can be extracted to a direction of the board 123 by using the
p-contact electrode 118 made of transparent ITO and the board 123
made of a transparent material such as glass.
Eleventh Embodiment
(Composition of LED Element 101)
[0217] FIGS. 17A to 17C show an LED element in the eleventh
preferred embodiment according to the invention.
[0218] The LED element 101 is composed of five emission regions
disposed in the longitudinal direction as shown in FIG. 17A. It is
further composed of plural n-external electrodes 117 and p-external
electrodes 118. The p-external electrode 118 is, as shown in FIG.
17B, connected through an electrode connecting portion 118A to the
p-contact electrode 115 made of Rh.
[0219] Also in the elongated LED element 101, the n-external
electrode 117 and the p-external electrode 118 are provided at the
side of the element and have a bonding width to give a sufficient
bonding property. The n-external electrode 117 and the p-external
electrode 118 are disposed opposed to, each other at the longer
sides of the LED element 101. The n-external electrode 117 is
exposed at the shorter sides of the LED element 101.
[0220] The n-external electrode 117 and the p-external electrode
118 are flip-chip bonded on a wiring pattern of a board (not shown)
through a solder 120A as shown in FIG. 17C.
Effects of the Eleventh Embodiment
[0221] In the eleventh embodiment, in addition to the effects of
the tenth embodiment, the LED element 101 is suitable for a use in
need of a large amount of light since it is easy to form the wiring
on the LED element 101 though having the elongated structure. Also,
since the n-external electrode 117 and the p-external electrode 118
are provided with a given bonding with at the side of the LED
element 101, a uniform and good electrical bonding property can be
obtained.
[0222] Even when the plural emission regions are provided as shown
in FIG. 17A, heat can be rapidly radiated from the GaN-based
semiconductor layer 200 to the mounting face (not shown) as
described in the tenth embodiment. Thus, a sufficient heat
radiation property can be offered even in a high-output LED element
101.
[0223] Although in the eleventh embodiment is explained the
elongated LED element 101 with the five emission regions, the
number, size and form of emission regions may be arbitrarily varied
according to use.
[0224] The LED element 101 is not limited to a use for the
flip-chip mounting, and it may be face-up mounted while making
modifications that the p-contact electrode 115 is made of a
transparent material such as ITO, ZnO, Au/Co and Ni/Ti and that the
sapphire substrate 110 is used as the mounting face.
Twelfth Embodiment
(Composition of LED Element 101)
[0225] FIGS. 18A and 18B show an LED element in the twelfth
preferred embodiment according to the invention.
[0226] The LED element 101 is a large size (1 mm square) LED
element. It is provided with an n-external electrode 117 that
extends like a comb from the side of the element into the emission
region and plural electrode connecting portions 118A to connect the
p-contact electrode 115 and the p-external electrode 118.
[0227] Also in the twelfth embodiment, the n-external electrode 117
and the p-external electrode 118 are exposed opposite to each other
at the side of the element and formed over the entire width of one
side of the element.
[0228] The p-contact electrode 115 may be made of a transparent
material when the LED element 101 is used to extract light from the
surface of the GaN-based semiconductor layer 200. In contrast, it
may be made of a reflective conductive material such as Rh other
than the transparent material when the LED element 101 is used to
extract light from the surface of the sapphire substrate 110.
Effects of the Twelfth Embodiment
[0229] In the twelfth embodiment, since the n-external electrode
117 and the p-external electrode 118 are disposed at the side of
the element not on the light extraction surface, the large size LED
element 101 can have an increased area to extract light from the
inside of the element so as to enhance the light extraction
efficiency.
[0230] Since the n-external electrode 117 and the p-external
electrode 118 are formed opposite to each other at the side of the
element, the bonding area to the external member or device can be
increased, thereby enhancing the bonding strength, the heat
radiation property and the uniformity in Current spreading.
Further, the LED element 101 can be securely mounted without
requiring a troublesome adjustment such as positioning in the
mounting as compared to an Au bump mounting.
[0231] Although in the large size LED element 101 the amount of
heat generation is increased as compared to a standard size LED
element, a sufficient heat radiation property can be secured since
the n-external electrode 117 and the p-external electrode lie are
disposed at the side of the element to be in close contact with the
mounting board.
[0232] Although in the twelfth embodiment the n-external electrode
117 and the p-external electrode 118 are disposed opposite to each
other at the side of the LED element 101 and formed over the entire
width of the side, these electrodes may be formed in arbitrary
position and size if the n-external electrode 117 and the
p-external electrode 118 are exposed at the side of the LED element
101 without being short-circuited each other.
[0233] Although in the twelfth embodiment the LED element 101 is
provided with the nine electrode connecting portions 118A, the
number, size and form of the electrode connecting portions 118A may
be arbitrarily varied according to use.
Thirteenth Embodiment
[0234] FIG. 19 shows an LED element in the thirteenth preferred
embodiment according to the invention.
[0235] The LED element 101 is formed such that the n-external
electrode 117 and the p-external electrode 118 are disposed along
the side of the large size LED element 101.
[0236] This structure can also enhance the bonding strength, the
heat radiation property and the uniformity in current spreading as
described in the twelfth embodiment.
Fourteenth Embodiment
[0237] FIG. 20 shows an LED element in the fourteenth preferred
embodiment according to the invention.
[0238] The LED element 101 is formed such that the n-external
electrode 117 and the p-external electrode 118 are disposed
opposite to each other at the side of the large size LED element
101 and formed extending like a comb toward the center of the LED
element 101 from the side.
[0239] This structure can also enhance the bonding strength and the
heat radiation property as described in the twelfth embodiment.
[0240] Further, since the n-external electrode 117 and the
p-external electrode 118 are formed extending like a comb, the
uniformity in current spreading can be further enhanced.
Fifteenth Embodiment
(Mounting Structure of LED Element 101)
[0241] FIG. 21 is a cross sectional view showing a mounting
structure of an LED element in the fifteenth preferred embodiment
according to the invention, where the LED element 101 is connected
to a copper lead 121.
[0242] The copper lead 121 is made by forming a copper alloy
material into a lead form by pressing etc. It is connected to the
n-external electrode 117 and the p-external electrode 118 at the
side of the LED element 101 by the solder bonding with solder
plating 120.
[0243] The LED element 101 is provided with the p-contact electrode
115 made of Rh so as to extract light from the surface of the
sapphire substrate 110.
[0244] Although the n-GaN layer 112 is at a side thereof in face
contact with the copper leads 121, 121 to supply current to the
anode side and the cathode side, short-circuiting does not occur
since it is not in ohmic contact with them at the contact face.
[0245] As shown in FIG. 21, one pair of the copper leads 121, 121
serve as an electrical connection and a mechanical support, and the
LED element 101 is suspended supported by the copper leads 121,
121.
[0246] In order to protect the LED element 101 and the copper lead
121 and to enhance the light extraction efficiency, it is desirable
that the LED element 101 and the copper lead 121 are integrally
sealed with a seal resin such as epoxy resin.
[0247] The solder plating 120 may be replaced by a conductive
bonding material to electrically connect the copper lead 1201 and
the LED element 101. Such a conductive bonding material includes,
e.g., epoxy adhesive containing Ag paste or a conductive
filler.
(Operation of the LED Element 101)
[0248] When power is supplied connecting the copper lead 121 on to
a power supply (not shown), a forward voltage is applied through
the n-external electrode 117 and the p-external electrode 118 of
the LED element 101 to the light-emitting layer 113. Thereby,
radiative recombination of hole and electron occurs in the
light-emitting layer 113 and blue light is emitted. Blue light
irradiated to the sapphire substrate 110 side is externally
radiated passing through the sapphire substrate 110. In contrast,
blue light irradiated to the p-contact electrode 115 side is
reflected on the p-contact electrode 115 and then externally
radiated passing through the sapphire substrate 110
Effects of the Fifteenth Embodiment
[0249] The effects of the fifteenth embodiment are as follows.
[0250] (1) Since the n-external electrode 117 and the p-external
electrode 118 are disposed at the side of the LED element 101 not
on the light extraction surface, another type of mounting other
than face-up and flip-chip can be realized as shown in FIG. 21.
Thus, the mounting structure can be low-profile and compact and the
package with a seal material can be enhanced in sealability and
downsized. It is more desirable that the copper lead 121 is in
height lower than the LED element 101 to enhance the light
extraction efficiency from the side face. [0251] (2) Since the
copper lead 121 with a good thermal conductivity is disposed at the
side of the element, heat generated during the operation can be
rapidly radiated through the GaN-based semiconductor layer 200 and
the solder plating 120 without blocking the external radiation of
emitted light of the LED element 101.
[0252] In the fifteenth embodiment the LED element 101 is provided
with the p-contact electrode 115 made of Rh. However, when the
p-contact electrode 115 is made of a transparent material such as
ITO, light can be extracted from any of the surface of the sapphire
substrate 110 and the surface of the GaN-based semiconductor layer
200.
Sixteenth Embodiment
(Mounting Structure of LED Element 101)
[0253] FIG. 22A is a cross sectional view showing a first mounting
structure of an LED element 101 in the sixteenth preferred
embodiment according to the invention.
[0254] As shown in FIG. 22A, the LED element 101 is provided with
the p-contact electrode 115 made of a transparent material such as
ITO. The sapphire substrate 110 is at the bottom face bonded to the
insulative board 123 made of Al.sub.2O.sub.3 through an adhesive
(not shown). The n-external electrode 117 and the p-external
electrode 118 are electrically connected through the solder 120A to
the wiring pattern 122 formed on the surface of the board 123.
[0255] The solder 120A may be replaced by a conductive adhesive
such as Ag paste and epoxy adhesive containing a conductive filler.
The conductive adhesive may be transparent. For example, if a
transparent epoxy resin containing a conductive filler is used,
light can be extracted from the side of the LED element 101.
[0256] The board 123 may be transparent. In this case, light is can
be extracted from the surface of the GaN-based semiconductor layer
200 and from the surface of the sapphire substrate 110 toward the
board 123.
[0257] The board 123 may be made of a conductive material such as
Cu and Al. In this case, although an insulation layer needs to be
formed on the surface to prevent the short-circuiting through the
board 123, it is effective to choose the conductive material to
secure a heat radiation property.
[0258] FIG. 22B is a cross sectional view showing a second mounting
structure of an LED element in the sixteenth embodiment according
to the invention.
[0259] The second mounting structure is different from the first
structure in that the LED element 101 is placed in a concave
portion 123A formed in the board 123.
[0260] The concave portion 123A is provided with a slope 123B so as
to have a space around the LED element 101. Since the LED element
101 is placed in the concave portion 123A, the amount of protrusion
from the surface of the board 123 can be reduced. The LED element
101 is electrically connected through the solder 120A embedded in
the space formed between the slope 123B and the LED element 101 to
a pair of wiring patterns 122.
[0261] The board 123 in FIG. 22B may be made of a metal material
with a light reflection property. In this case, although an
insulation layer is formed on the surface, light irradiated to the
side direction of the LED element 101 can be reflected on the
reflective slope 123B so as to be extracted upward. Further, the
solder 120A may be a transparent and conductive adhesive to enable
the light extraction even in the electrical connection portion
Effects of the Sixteenth Embodiment
[0262] (1) In the first mounting structure, since the electrical
connection is made through the solder 120A to the n-external
electrode 117 and the p-external electrode 118 formed at the side
of the LED element 101, the light extraction area from the
GaN-based semiconductor layer 200 can be increased. The electrical
connection at the side of the element may be made through the
conductive adhesive etc. instead of the solder 120A Thus, a
suitable way of bonding can be chosen according to use. Further,
when the board 123 is made of a transparent material, light can be
extracted from the surface of the board 123. [0263] (2) In the
second mounting structure, in addition to the effects of the first
mounting structure, since the LED element 101 is place in the
concave portion 123A of he board 123, the LED element 101 can be
easily positioned and made low-profile by reducing the amount of
protrusion from the surface of the board 123. Further, since the
concave portion 123A is provided with the slope 123B, light
irradiated to the side direction of the LED element 101 can be
reflected on the slope 123b to be extracted upward.
Seventeenth Embodiment
[0263] (Mounting Structure of LED Element 101)
[0264] FIG. 23 is a cross sectional view showing a mounting
structure of an LED element in the seventeenth preferred embodiment
according to the invention.
[0265] The LED element 101 of the seventeenth embodiment is
different from the LED element 101 in FIG. 16A in that the sapphire
substrate 110 is lifted off.
[0266] The LED element 101 is prepared by lifting off the sapphire
is substrate 110 and the AlN buffer layer 111 by irradiating laser
light toward the surface of the sapphire substrate 110. Meanwhile,
after the lift-off, the AlN buffer layer 111 may be left on the
surface of the n-GaN layer 112. In such a case, it is desirable
that the remaining AlN buffer layer 111 is removed by acid
cleaning.
[0267] In operation, when power is supplied connecting the wiring
pattern 122 to a power supply (not shown), a forward voltage is
applied through the n-external electrode 117 and the p-external
electrode 118 of the LED element 101 to the light-emitting layer
113. Thereby, radiative recombination of hole and electron occurs
in the light-emitting layer 113 and blue light is emitted. Blue
light irradiated to the n-GaN layer 112 is externally radiated
passing through the n-GaN layer 112. In contrast, blue light
irradiated to the p-contact electrode 115 is reflected on the
p-contact electrode 115 made of Rh and then externally radiated
passing through the n-GaN layer 112.
[0268] The p-contact electrode 115 may be made of a transparent
material such as ITO if the board 123 is made of a transparent
material. Thereby, light can be extracted from the bottom side of
the GaN-based semiconductor layer 200.
Effects of the Seventeenth Embodiment
[0269] In the seventeenth embodiment, light can be extracted from
the n-GaN layer 112 of the flip-chip mounted LED element 101.
Therefore, the intra-layer confined light being not externally
radiated from the GaN-based semiconductor layer 200 can be reduced
so as to enhance the external radiation efficiency.
[0270] Further, since the n-external electrode 117 and the
p-external electrode 118 are disposed at the side of the LED
element 101, the LED element 101 can be low profiled to meet the
downsizing of a mounted object or to avoid a restriction caused by
the form of a mounted object. Further, the heat radiation property
through the insulation layer 119 to the board 123 can be
enhanced.
[0271] In view of the protection of the LED element 101, it is
desirable that the n-GaN layer 112 is covered with a transparent
material or sealed with a seal material such as epoxy resin as well
as the wiring pattern 122 and the board 123.
[0272] The n-GaN layer 112 may be provided with an uneven surface
to reduce the intra-layer confined light to enhance the external
radiation efficiency.
Eighteenth Embodiment
(Mounting Structure of LED Element 101)
[0273] FIG. 24 is a cross sectional view showing a mounting
structure of an LED element in the eighteenth preferred embodiment
according to the invention.
[0274] The LED element 101 is composed such that a glass member 130
with a high refractive index and a wiring pattern 122 is bonded
through a transparent adhesive 142 onto the surface of the n-GaN
layer 112 of the LED element 101 as shown in FIG. 23.
[0275] The p-contact electrode 115 of the LED element 101 is made
of Rh.
[0276] The transparent adhesive 142 is an epoxy adhesive which does
not block the transmission of light emitted from the LED element
101.
[0277] The n-external electrode 117 and the p-external electrode
118 are electrically connected through the transparent and
conductive adhesive 142 to the wiring pattern 122. The adhesive 142
can be, as described earlier, epoxy resin containing a conductive
filler.
[0278] In operation, when power is supplied connecting the wiring
pattern 122 to a power supply (not shown), a forward voltage is
applied through the n-external electrode 117 and the p-external
electrode 118 of the LED element 101 to the light-emitting layer
113. Thereby, radiative recombination of hole and electron occurs
in the light-emitting layer 113 and blue light is emitted. Blue
light irradiated to the n-GaN layer 112 is externally radiated
passing through the n-GaN layer 112, the transparent adhesive 142
and then the glass member 130. In contrast, blue light irradiated
to the p-contact electrode 115 is reflected on the p-contact
electrode 115 made of Rh and then externally radiated passing
through the n-GaN layer 112, the transparent adhesive 142 and then
the glass member 130.
[0279] On the other hand, a light component reflected on the
interface of the glass member 130 and then laterally propagated
through the GaN-based semiconductor layer 200 can be externally
radiated after it is entered into an adhesive 120B from the side of
the LED element 101.
Effects of the Eighteenth Embodiment
[0280] In the eighteenth embodiment, since the LED element 101 is
bonded through the transparent adhesive 142 onto the glass member
130, a light source suitable for a transmitting illumination such
as a backlight can be offered.
[0281] Although in the eighteenth embodiment the p-contact
electrode 115 is made of Rh with a light reflecting property, it
may be made of a transparent material such as ITO so as to also
extract light from the bottom of the GaN-based semiconductor layer
200.
Nineteenth Embodiment
(Composition of LED Element 101)
[0282] FIG. 25A is a cross sectional view showing a large-size LED
element (1 mm square) in the nineteenth preferred embodiment
according to the invention. FIG. 25B is a top view showing the LED
element in FIG. 25A, which is viewed from the side of an insulation
layer formation surface thereof.
[0283] The LED element 101 is, as shown in FIG. 25B, composed of: a
hole 101A which is formed at the center of the element and in the
depth direction from the p-GaN layer 114 to the n-GaN layer 112; an
n-external electrode 117 formed covering the n-GaN layer 112
exposed by etching inside the hole 10A; and a p-external electrode
118 formed covering the periphery of the GaN-based semiconductor
layer 200 and electrically connected to the p-contact electrode
115. The p-contact electrode 115 of the LED element 101 is made of
Rh.
[0284] The LED element 101 can be flip-chip bonded onto a board
(not shown) which is provided with a wiring pattern corresponding
to a pattern of solder plating that corresponds to the n-external
electrode 117 and the p-external electrode 118.
Effects of the Nineteenth Embodiment
[0285] In the nineteenth embodiment, since the n-external electrode
117 is disposed at the center of the element and the p-external
electrode 118 are formed on the periphery of the element, even the
large size LED element 101 can render the entire surface of the
light-emitting layer 113 uniformly emit light.
[0286] By flip-chip mounting the LED element 101, a good emission
property can be obtained while securing a good heat radiation
property to the mounting board etc.
[0287] In the nineteenth embodiment, when the LED element 101 is
mounted in face-up disposition, the p-contact electrode 115 may be
made of a transparent material such as ITO. Thereby, a good wire
bonding property can be obtained while preventing a reduction in
light extraction efficiency as much as possible in the case of the
face-up mounting.
[0288] Although the abovementioned embodiments relate to the light
emitting element (=LED element), the invention is not limited to
the light emitting element and may be applied to another optical
element (or device) such as a solar cell and a light-receiving
element and a method of making the same.
[0289] Although the invention has been described with respect to
the specific embodiments for complete and clear disclosure, the
appended claims are not to be thus limited but are to be construed
as embodying all modifications and alternative constructions that
may occur to one skilled in the art which fairly fall within the
basic teaching herein set forth.
* * * * *